The present invention relates to a thin film capacitor and in particular to such a capacitor provided with protection against damage that can be caused by the application of voltages in excess of the maximum intended operating voltage of the capacitor. This can occur, for example, during an electrostatic discharge event.
Electronic components in general can be damaged when they are subjected to voltages greater than their intended operating voltage as may occur when a build up of electrostatic charge is applied to that component. In the case where the component is a capacitor, as the applied voltage increases above the maximum intended operating voltage of the capacitor, a point is reached where the dielectric of the capacitor begins to conduct. This causes heating of the capacitor dielectric and eventual failure of the component. Components are particularly vulnerable to electrostatic discharge damage when being handled, for example during assembly of the component onto a printed circuit board.
IBM Technical Disclosure Bulletin, Volume 24, Number 11B at page 6040 to 6041 discloses connecting a diode across a thin film decoupling capacitor to prevent damage occurring to the capacitor due to an electrostatic discharge event. The diode is formed using a p-n junction in a silicon substrate of the capacitor.
In this case it is necessary to use a silicon substrate and to include dopants for the p-type and n-type conductivities. The introduction of such dopants in the reaction chamber can be a source of contamination to other parts of the device being fabricated, and the manufacture of such a device is complex and expensive.
In accordance with the present invention there is provided a thin film capacitor comprising a thin film structure on an insulating substrate, wherein the thin film structure provides a capacitor element including a dielectric film of the capacitor, and first and second conductive film portions which each provide a capacitor plate, and wherein the thin film structure also provides a protection element connected electrically in parallel with the capacitor element, the protection element having a conduction path that operates at a voltage lower than the breakdown voltage of the capacitor dielectric film.
This thin film structure in accordance with the invention is advantageous for protecting the thin film capacitor against damage that may otherwise result due to the application of a voltage in excess of the intended operating voltage of the capacitor. Preferably at least one of the first and second conductive film portions also provides an electrode of the protection element. This feature offers the advantages of simplified fabrication, a compact structure and an opportunity to produce the thin film capacitor at low cost.
The protection element may be a thin film diode. The diode may include, for example, a material of silicon rich non-stoichiometric silicon nitride. A number of such devices may be connected in series.
Other forms of the protection element may include, for example a discharge gap or a resistive element between conductive film portions. These conductive film portions may comprise third and fourth conductive film portions, the third conductive film portion is in electrical connection with one of the first and second conductive film portions, and the fourth conductive film portion is in electrical connection with the other one of the first and second conductive film portions. Each of the third and fourth conductive film portions may be integral with it""s associated first or second conductive film portion.
Other aspects and optional features of the present invention appear in the appended claims.
Thus, in accordance with the present invention the thin film capacitor element has an associated thin film protection element.
Furthermore, the thin film capacitor element has an associated thin film protection element that may be produced on the same substrate. The substrate may be an arbitrary insulating material.